Enhanced layer 1-layer 2 (L1/L2) triggered mobility (LTM) handover (HO) procedure

Abstract

A Layer 1-Layer 2 (L1/L2) Triggered Mobility (LTM) handover (HO) procedure, and method. A gNB-Centralized Unit User Plane (gNB-CU-CP) sends Radio Resource Control (RRC) messages with LTM candidate cell configuration of LTM candidate gNB-DUs. Based on the RRC messages, a Layer (L1) Measurement Report is sent to the LTM candidate gNB-DUs. In response, the LTM candidate gNB-DUs determine whether a radio condition of the LTM candidate gNB-DUs meet a predetermined resource reservation criteria. Based on meeting the predetermined resource reservation criteria, the LTM candidate gNB-DUs initiate reservation of radio resources for an LTM candidate cell for a LTM cell switch. The LTM candidate gNB-DUs send to the gNB-CU-CP an updated LTM candidate cell configuration. The gNB-CU-CP sends the updated radio resource configuration to the UE via the serving gNB-DU.

What is claimed is: 
     
         1 . A method for preparing and executing a Layer 1-Layer 2 (L1/L2) Triggered Mobility (LTM) Handover (HO) procedure, comprising:
 receiving, a Layer 1 (L1) Measurement Report directly at one or more LTM candidate gNB-Distributed Units (gNB-DUs) from one of a User Equipment (UE) or a serving gNB-DU, wherein the L1 Measurement Report is based on one or more Radio Resource Control (RRC) messages with an LTM candidate cell configuration of the one or more LTM candidate gNB-DUs sent earlier to the UE via a serving cell;   determining, by the one or more LTM candidate gNB-DUs in response to receiving the L1 Measurement Report, whether a radio condition of one of the one or more LTM candidate gNB-DUs meets a predetermined resource reservation criteria;   initiating, by the one or more LTM candidate gNB-DUs in response to the radio condition of the one or more LTM candidate gNB-DUs meeting the predetermined resource reservation criteria or in response to the UE performing Uplink (UL) Synchronization by sending a Random-Access CHannel (RACH) request to the one or more LTM candidate gNB-DUs to acquire timing advance, reservation of partial or full radio resources for one of one or more LTM candidate cells for a LTM cell switch from the serving cell to the one of the one or more LTM candidate cells by the UE; and   sending an updated radio resource configuration for the one or more LTM candidate cells having the reserved partial or full radio resources of the one or more LTM candidate cells to the UE via the serving gNB-DU.   
     
     
         2 . The method of  claim 1 , wherein the determining whether the radio condition of the one of the one or more LTM candidate gNB-DUs meets the predetermined resource reservation criteria further comprises determining at least whether L1 measurements of the one of the one or more LTM candidate cells are greater than a pre-defined Reference Signals Received Power (RSRP) threshold. 
     
     
         3 . The method of  claim 1  further comprises the one or more candidate gNB-DUs initiating data forwarding from a gNB-Centralized Unit User Plane (gNB-CU-UP) to the one or more LTM candidate gNB-DUs, based on the radio condition of the one of the one or more LTM candidate gNB-DUs, as reported by the UE, meeting the predetermined resource reservation criteria. 
     
     
         4 . The method of  claim 3  further comprises determining the radio condition of the one of the one or more LTM candidate gNB-DUs drops below the predetermined resource reservation criteria, and, in response, stopping the data forwarding of data to the one of the one or more LTM candidate gNB-DUs. 
     
     
         5 . The method of  claim 3 , wherein the initiating, by the one or more LTM candidate gNB-DUs, the reservation of the partial or full radio resources at the one of the one or more LTM candidate cells of the UE comprises initiating reservation of at least Random Access Channel (RACH) resources comprising a RACH preamble of the one of the one or more LTM candidate cells of the UE before the LTM cell switch from the serving cell to the one of the one of the one or more LTM candidate cells. 
     
     
         6 . The method of  claim 5 , wherein the initiating, by the one or more LTM candidate gNB-DUs, reservation of the at least RACH resources of the one of the one or more LTM candidate cells of the UE comprises initiating reservation of the at least RACH resources of the one of the one or more LTM candidate cells of the UE comprising the RACH preamble corresponding to a best beam or a best beam-group of the one of the one or more LTM candidate cells for the UE, based on the L1 measurement report. 
     
     
         7 . The method of  claim 3 , wherein the initiating the data forwarding from the gNB-CU-UP to the one or more LTM candidate gNB-DUs is triggered based on receiving, at the gNB-CU-UP, a control-Protocol Data Unit (PDU) from the one of the one or more LTM candidate gNB-DUs or a signaling message from the one of the one or more LTM candidate gNB-DUs via a gNB Centralized Unit (gNB-CU) over F1 and E1 interfaces respectively. 
     
     
         8 . The method of  claim 1 , further comprising:
 prior to receiving the L1 Measurement Report:
 configuring the UE for L1/L2 Triggered Mobility (LTM) with the one or more LTM candidate cells; 
 receiving, at a gNB-Centralized Unit User Plane (gNB-CU-UP), Layer 3 (L3) RRC Measurements from the UE; and 
 sending one or more RRC Reconfiguration messages with LTM Candidate Cell Configuration of the one or more LTM candidate cells to the UE via the serving gNB-DU. 
   
     
     
         9 . A Next Generation-Radio Access Network (NG-RAN) Node comprising a candidate distributed unit (DU), the candidate DU comprising:
 a memory storing computer-readable instructions; and   a processor connected to the memory, wherein the processor is configured to execute the computer-readable instructions to perform operations to:
 receive a Layer 1 (L1) Measurement Report directly at one or more Layer 1-Layer 2 (L1/L2) Triggered Mobility (LTM) candidate gNB-Distributed Units (gNB-DUs) from one of a User Equipment (UE) or a serving gNB-DU via the gNB-CU, wherein the L1 Measurement Report is based on one or more Radio Resource Control (RRC) messages with an LTM candidate cell configuration of one or more LTM candidate gNB-DUs sent earlier to the UE via a serving cell; 
 determine, in response to receiving the L1 Measurement Report, whether a radio condition of one of the one or more LTM candidate gNB-DUs meets a predetermined resource reservation criteria; 
 initiate, at the one or more LTM candidate gNB-DUs in response to the radio condition of the one of the one or more LTM candidate gNB-DUs meeting the predetermined resource reservation criteria or in response to the UE performing Uplink (UL) Synchronization by sending a Random-Access CHannel (RACH) request to the one or more candidate gNB-DUs to acquire timing advance of candidate cell, reservation of partial or full radio resources for one of one or more LTM candidate cells for an LTM cell switch from the serving cell to the one of the one or more LTM candidate cells by the UE; and 
 send an updated radio resource configuration for the one or more candidate cells having the partial or full radio resources of the one or more LTM candidate cells to the UE via the serving gNB-DU. 
   
     
     
         10 . The NG-RAN Node of  claim 9 , wherein the processor is configured to determine whether the radio condition of the one of the one or more LTM candidate gNB-DUs meets the predetermined resource reservation criteria by determining at least whether L1 measurements of the one of the one or more LTM candidate cells are greater than a pre-defined Reference Signals Received Power (RSRP) threshold. 
     
     
         11 . The NG-RAN Node of  claim 9 , wherein the processor is configured to initiate data forwarding to one of the one or more LTM candidate gNB-DUs, based on the radio condition of the one of the one or more LTM candidate gNB-DUs, as reported by the UE, meeting the predetermined resource reservation criteria. 
     
     
         12 . The NG-RAN Node of  claim 11 , wherein the processor is further configured to determine the radio condition of the one of the one or more LTM candidate gNB-DUs drops below the predetermined resource reservation criteria, and, in response, stop the data forwarding of data to the one of the one or more LTM candidate gNB-DUs. 
     
     
         13 . The NG-RAN Node of  claim 11 , wherein the processor is configured to initiate, at the one or more LTM candidate gNB-DUs, the reservation of the partial or full radio resources at the one of the one or more LTM candidate cells of the UE by initiating reservation of Random Access Channel (RACH) resources comprising a RACH preamble of the one of the one or more LTM candidate cells of the UE before the LTM cell switch from the serving cell to the one of the one of the one or more LTM candidate cells. 
     
     
         14 . The NG-RAN Node of  claim 13 , wherein the processor is configured to initiate, at the one or more LTM candidate gNB-DUs, reservation of the at least RACH resources of the one of the one or more LTM candidate cells of the UE by initiating reservation of the at least RACH resources of the one of the one or more LTM candidate cells of the UE comprising the RACH preamble corresponding to a best beam or a best beam-group of the one or more LTM candidate cells for the UE, based on the L1 measurement report. 
     
     
         15 . The NG-RAN Node of  claim 11 , wherein the processor is configured to initiate the data forwarding from a gNB Centralized Unit User Plane (gNB-CU-UP) to the one or more LTM candidate gNB-DUs based on receiving a control-Protocol Data Unit (PDU) from the one of the one or more LTM candidate gNB-DUs or a signaling message from the one of the one or more LTM candidate gNB-DUs via a gNB Centralized Unit Control Plane (gNB-CU-CP) over F1 and E1 interfaces respectively. 
     
     
         16 . The NG-RAN Node of  claim 9 , wherein the processor is further configured to:
 prior to receiving the L1 Measurement Report:
 configure the UE for L1/L2 Triggered Mobility (LTM) with the one or more LTM candidate cells; 
 receive Layer 3 (L3) RRC Measurements from the UE; and 
 send one or more RRC Reconfiguration messages with LTM Candidate Cell Configuration of the one or more LTM candidate cells to the UE. 
   
     
     
         17 . A non-transitory computer-readable media medium having computer-readable instructions stored thereon, which when executed by a processor causes the processor to perform operations comprising:
 receiving, a Layer 1 (L1) Measurement Report directly at one or more LTM candidate gNB-Distributed Units (gNB-DUs) from one of a User Equipment (UE) or a serving gNB-DU, wherein the L1 Measurement Report is based on one or more Radio Resource Control (RRC) messages with an LTM candidate cell configuration of the one or more LTM candidate gNB-DUs sent earlier to the UE via a serving cell;   determining, by the one or more LTM candidate gNB-DUs in response to receiving the L1 Measurement Report, whether a radio condition of one of the one or more LTM candidate gNB-DUs meets a predetermined resource reservation criteria;   initiating, by the one or more LTM candidate gNB-DUs in response to the radio condition of the one or more LTM candidate gNB-DUs meeting the predetermined resource reservation criteria or in response to the UE performing Uplink (UL) Synchronization by sending a Random-Access CHannel (RACH) request to the one or more LTM candidate gNB-DUs to acquire timing advance, reservation of partial or full radio resources for one of one or more LTM candidate cells for a LTM cell switch from the serving cell to the one of the one or more LTM candidate cells by the UE; and   sending an updated radio resource configuration for the one or more candidate cells having the partial or full radio resources of the one or more LTM candidate cells to the UE via the serving gNB-DU.   
     
     
         18 . The non-transitory computer-readable medium of  claim 17 , wherein the determining whether the radio condition of the one of the one or more LTM candidate gNB-DUs meets the predetermined resource reservation criteria further comprises determining at least whether L1 measurements of the one of the one or more LTM candidate cells are greater than a pre-defined Reference Signals Received Power (RSRP) threshold. 
     
     
         19 . The non-transitory computer-readable medium of  claim 17 , wherein the operations further comprise the one or more candidate gNB-DUs initiating data forwarding from a gNB-Centralized Unit User Plane (gNB-CU-UP) to the one or more LTM candidate gNB-DUs, based on the radio condition of the one of the one or more LTM candidate gNB-DUs, as reported by the UE, meeting the predetermined resource reservation criteria. 
     
     
         20 . The non-transitory computer-readable medium of  claim 19 , wherein the operations further comprise determining the radio condition of the one of the one or more LTM candidate gNB-DUs drops below the predetermined resource reservation criteria, and, in response, stopping the data forwarding of data to the one of the one or more LTM candidate gNB-DUs.